1) Field of the Invention
The invention relates to an element for the frictional connection of components.
2) Background Art
Frictional connections are used in all sectors of mechanical engineering, often to transmit transverse forces or torque. The magnitude of the force which can be transmitted in each case depends, in addition to the design features, primarily on the coefficient of static friction (friction coefficient) of the component surfaces which are joined to one another. Steel/steel pairings typically have friction coefficients of 0.15, which is frequently insufficient to provide a reliable frictional connection given the increasingly rising demands placed on machine components.
Measures for increasing the friction coefficient, e.g. in shrink joints, have been known from the very early times of mechanical engineering; for example, as early as 1860 it was recommended to introduce sand in the joint gap, in order to improve the seating of gearwheels on shafts. The grains of sand are pressed into the surfaces of the components to be joined together under the effect of the shrink forces and bring about a certain form fit, with sand grain penetration depths of a few tenths of a millimeter. In practice, however, it is difficult to incorporate loose particles or particles which have been mixed in a spreadable carrier media evenly into the joint gap.
Although this method is effective in principle, the effect of relatively coarse particles in the joint gap entails an increased risk of long-term fracture. If the prevailing operating conditions indicate that such a risk exists, the impressions which the particles, used for force transmission, make in the component surfaces must not be significantly deeper than the peak-to-valley heights caused by prior machining.
Various methods are known for incorporating hard particles uniformly and reproducibly in a joint gap. DOS 23 64 275 of 07.10.1975 (corresponds to GB 1,483,124) describes the application of a layer containing hard-material bodies onto one of two interacting surfaces by vapor deposition, spraying on, sintering on or diffusion of a foreign material into the component surface.
In xe2x80x9cant-Antriebstechnik [Drive Engineering]xe2x80x9d 20, No. 1-2, January-February 1981, Peeken, et al propose surface layers, for the frictional transmission of moments, which are produced using an electrodeposition method by jointly depositing fine grains of hard material and a metallic binding phase. By means of such layers, the static friction of a shaft-hub shrink joint is more than doubled. These layers even allow the friction coefficients under rotating flexural loading to be even better than under purely static loading.
The measures described to date for increasing the static friction coefficient are all based on directly covering one of the two components to be connected with friction-increasing layers. However, in practice, the desired coating often cannot be applied to either of the two components for process engineering reasons.
Swiss Patent Specification 192 197 discloses paper or linen as flexible carrier material for a layer containing grains of hard material and applied on both sides. Described as an active mechanism for increasing the adhesion is a mechanical pushing of wedge-shaped particles of hard material one above another by means of relative movement of the components to be connected. JP 6-147206 also discloses paper or linen as a flexible carrier material for grains of hard material. The connecting elements named in the documents are not capable of transmitting high transverse forces. They are therefore unsuitable for many applications.
DE 31 49 596 A1 discloses a connection which is produced by using coarse grains of hard material. A description is given of the use of an elastic supporting film which is made from a deformable material and does not itself participate in the transmission of force. It is disadvantageous that this connection is not detachable and therefore does not permit a reversible connection of the workpieces to be joined together.
The present invention is based on the object of providing a friction-increasing reversible connection, which is free from play, between workpieces to be joined together, which connection avoids the drawbacks of the prior art.
This object is achieved according to the invention by means of a connection element which comprises a thin, resilient film with an inherent strength which is at least as high as the inherent strength of the workpieces to be joined together, the resilient film bearing particles of defined size at its surface and these particles consisting of a material with a compressive and shear strength which exceeds that of the workpieces to be joined together The particles of a material with a compressive and shear strength which exceeds that of the workpieces to be joined together are referred to herein as hard particles. Thin films are preferably to be understood as meaning films with a thickness of xe2x89xa60.2 mm.
The connecting element according to the invention, which is also referred to as friction film/foil below has the following advantages over known frictional connections:
a) the difficulties associated with only a partial coating of relatively large or bulky components do not occur;
b) it permits the reversible connection of components which are not suitable for direct coating, even in cases where large transverse forces occur;
c) the friction coefficient of frictional connections is increased by at least 50%, usually even 100-200%;
d) it is economical to produce;
e) it is easy to adapt even to joint surfaces with a complex shape or to non-planar joint surfaces;
f) it does not require any significant additional expenditure during assembly